Table 3.

Risk of bias

	Design and description of comparison groups	Selection bias		Performance bias	Detection bias	Attrition bias	Reporting bias
Authors		Random sequence generation	Allocation concealment	Blinding participants/personnel	Blinding outcome assessment	Incomplete outcome data	Selective reporting	Other bias
Hjermann et al. [38]	RCT – lifestyle intervention; anti-smoking advice given individually to all smokers vs. usual care	Unclear	Low risk	High risk	Unclear	Low risk	Unclear	Unclear
McBride et al. [34]	3-group randomised controlled intervention; pregnant women; – Usual care (advice to quit and self-help guide), woman only group (usual care plus late-pregnancy relapse prevention kit and 6 counselling calls), Partner-assisted group (woman only group intervention plus their partners received telephone counselling and a support guide)	Unclear	Unclear	High risk	Unclear	Low risk	Unclear	Unclear
McIntyre-Kingsolver et al. [39]	RCT - a multi-component cognitive-behavioral smoking program vs. the same program with spouses attending and receiving training designed to increase spouse social support	High risk	Unclear	High risk	Unclear	High risk	Unclear	High risk
Nyborg and Nevid [41]	3-group, randomly assigned; effort only control (written materials), therapist administered treatment (couples received weekly counselling sessions), self-administered/minimal contact control (behavioural treatment manual and weekly telephone contact)	Unclear	Unclear	High risk	Unclear	Unclear	Unclear	Unclear
Øien et al. [36]	Controlled, prospective, intervention study of two cohorts - a prenatal, structured, multi-disciplinary smoking cessation programme vs. common, nationwide recommended, advice on lifestyle, including smoking behaviour	N/A – not RCT	N/A	High risk	Unclear	Unclear	Unclear	High risk
Patten et al. [40]	Pilot, feasibility RCT - a web-based support skills training vs. health education	Unclear	Unclear	High risk	Unclear	Low risk	Low risk	Unclear
de Vries et al. [35]	Cluster RCT - Midwives in the experimental group provided brief health counseling, self-help materials on smoking cessation during pregnancy and early postpartum, and a partner booklet. Controls received routine care	Low risk	Unclear	High risk	Unclear	Low risk	Unclear	High risk
Wood et al. [37]	Cluster RCT – a nurse-coordinated multidisciplinary, family-based preventive cardiology programme vs. usual care	Unclear	Unclear	High risk	Unclear	High risk	Low risk	Low risk